The Influence Of Doping On Phase Transition Temperature Of CH₃NH₃PbI₃ And Photoelectric Properties Of Perovskite Solar Cells

Hybrid organic-inorganic perovskite solar cells are based on perovskite materials with ABX₃ perovskite structure as the core constitute,which play role in optical absorption and electron-hole transport material.The rapid emergence of solar cells based on hybrid organic-inorganic perovskites has recently received significant attention in the photovoltaic community due to their many advantages including low cost,facile preparation process,good stability,and high power conversion efficiency higher than20%?PCE?.Perovskite solar cells in n-i-p configurations are composed of three parts,which are electron transport layer,perovskite layer and hole transport layer.Recently,multiple cation and ions replacement in A-site,B-site or X-site,such as CsPbI₃?CH₃NH₃SnI₃ and CH₃NH₃PbBr₃,have demonstrated favorable stability with high power conversion efficiencies?PCE?.Due to the single composition in replacement,the physical properties of the perovskite material cannot be modulated.In this study,we sought to change the concentration and varieties of dopant into CH₃NH₃PbI₃ to modify the physical properties of perovskite material,such as phase transition temperature,thermal stability and carrier density.Our systematic studies may shed light on the working mechanism of the devices and extend the application of devices.The main findings are as follows.1?Doping of 2.5%SnCl₂ into CH₃NH₃PbI₃ to improve the phase transition temperature from 57?to 90?.For organic–inorganic hybrid perovskite solar cells?PCSs?,phase of perovskite can transform from tetragonal to cubic,since it is hard to avoid a temperature increase for devices during operation.In this work,we proposed a method that can improve the phase transition temperature via SnCl₂ doping.The influence of the doping ratio of SnCl₂ on phase transition temperature and photoelectric properties is studied in detail.The perovskite samples were doped with 0⁵%SnCl₂ and we found that doping 2.5%SnCl₂ into CH₃NH₃PbI₃ perovskite can help increase the phase change temperature from 57?to 90?,the highest among the CH₃NH₃PbI₃perovskite reported,demonstrating amazing heating tolerance.The enhanced phase change temperature can be attributed to slightly improved crystal orientation and modified the interaction with the ions in the crystal network.Ultraviolet-visible?UV-Vis?absorbance spectra and Hall Effect measurement display that the doped samples can yields stronger intensity of light absorption and less electron recombination rate.Based on the doped provskite film,we prepared perovskite solar cells with planar structure.We found that the efficiency of the doped devices decrease,resulting from the carrier density rising from 1.139*1014 cm^-3to 1.408*1014 cm^-3.2?The influence of doped varieties on phase transition temperature of CH₃NH₃PbI₃perovskite.In this study,we doped different cations with 2.5%ratio into perovskite material.Utraviolet-visible?UV-Vis?absorbance spectra indicates that the doping of PbCl₂,CsI and PbBr₂ can reduce the phase transition temperature of CH₃NH₃PbI₃materials.By contrast,the doping of NaI,KSCN and CaI₂ can little change the phase transition temperature of CH₃NH₃PbI₃ materials.First principles calculation manifests that binding energies of CH3NH3⁺with different orientation are E_[001]=-51.9743 eV,E_[011]=-51.9861 eV and E_[111]=-51.9515 eV,respectively.The energy difference can be defined as E^[001]-E^[011]=11.8meV and E^[111]-E^[011]=34.6meV,respectively,which is in agreement with the experimental results.Our systematic studies may shed light on the mechanism of phase transformation of perovskite materials.3?The effects of doped ration of KSCN on the photovoltaic properties of planar perovskite solar cells.Based on the fact that phase transition temperature of CH₃NH₃PbI₃ perovskite doped with KSCN little change,we doped the sample with different concentration of KSCN and fabricated the planar perovskite solar cells via solution process.The doping ratio 5%KSCN displayed the largest grain size,the highest optical absorption and lowest carrier recombination rates,leading to the best device performance.These findings provide a facile approach to fabricate efficient and stable PSCs by low processing temperature in ambient air,both of which are highly preferred for future practical applications of PSCs.